As power and energy constraints in microelectronic applications become more and more challenging, one is seeking alternative and more power efficient ways of switching, for subsequent use in computing. A conventional switching device used in the semiconductor industry is a C-MOS transistor. To overcome power-related bottlenecks in C-MOS devices, various switching devices which operate on fundamentally different transport mechanisms such as tunneling were investigated. However, combining the desirable characteristics of high on-current, very low off-current, abrupt switching, high speed as well as a small footprint in a device that might be easily interfaced to a C-MOS device is a challenging task. Mechanical switches such as nano-electromechanical switches (NEM switches) are promising devices to meet these kinds of criteria. A nano-electromechanical switch having a narrow gap between electrodes can be controlled by electrostatic actuation. In response to an electrostatic force a contact electrode can be moved or bent to contact another electrode thus closing the switch. The control of the narrow gap for the electrostatic actuation and for the electrical contact separation is a main issue in designing and operating nano-electromechanical switches. A nano-electromechanical switch typically has to meet both the requirement of high switching speed and low actuation voltage.
Common electromechanical switches use straight cantilever beams as switching elements. As the applicant has demonstrated, such solutions can be improved by using a NEM switch including: an actuator electrode and a curved cantilever beam flexing in response to an activation voltage (applied between the actuator electrode and the curved cantilever beam) for ensuring electrical contact between the curved cantilever beam and an output electrode of the switch. Such a switch can further be designed such that before, during and after flexing the curved cantilever beam, a gap remains between the curved cantilever beam and the actuator electrode, which is substantially uniform across the two facing electrodes and optimized for a minimum field in the closed state to minimize the switching energy of the device. The flexing may for instance occur mainly in a hinge portion of said cantilever beam connecting the curved cantilever beam with an input electrode of the NEM switch and the motion of the curved cantilever beam can be approximated as a rotation around the flexible hinge.
Today, NEM switches are notably contemplated for use as relays, transistors, logic devices and sensors. They are very attractive due to very low leakage currents as well as very high ON/OFF ratio. NEM switch technology is expected to complement the established CMOS technology, at least in several niche application areas.
A key challenge for NEM switches is the electrical contact quality; reliability is a related concern. Other potential issues to consider are: stiction/adhesion; wear and tear due to mechanical actuation, resulting in changes in the effective electrical contact area with time; and damages caused by electrical discharge (ablation or localized melting due to parasitic capacitive discharge while closing the switch), a thing that may become of particular when the contact resistance is very small. High contact resistance on the other hand leads to high power consumption, increased delay and decreased signal-to-noise ratios (SNRs).